Technical Field
This disclosure generally relates to a system comprising a touch sensor on polymer lens and methods for manufacturing such system.
Description of Related Art
Since touch screens provide an easy interface for human-machine interactions, they recently have found wide range of applications in consumer electronics, such as mobile phones, tablets, global positioning systems (GPS), medical devices, laptops, point-of-sale terminals, point-of-information kiosks, industrial control units, and visual display systems.
Among many types of touch screens, capacitive touch screens are getting more popular as compared to resistive touch screens due to their higher sensitivity to finger touch and good visibility for displays. The capacitive touch screens also allow users to perform functions not possible with resistive touch screens such as changing the orientation of images with thumb and forefinger since they can support multi touch capability. For a summary of touch screen technologies and their features, for example, see publications by: Alfred Poor “How It Works: The Technology of Touch Screens” Computerworld, Oct. 17, 2012; Geoff Walker “Fundamentals of Touch Technologies” 2013 SID Touch Gesture Motion Conference, October 2013; and Trevor Davis “Reducing Capacitive Touchscreen Cost in Mobile Phones” Embedded, Feb. 25, 2013. The entire content of these publications is incorporated herein by reference.
A capacitive touch screen system typically comprises a cover glass (or lens) with a screen printed decorative frame, and a touch sensor made from indium tin oxide (ITO) film deposited on another glass substrate. These two components are separately manufactured and assembled to form a single component by using an optically clear adhesive (OCA). Manufacturing of the currently available capacitive touch sensor involves in several process steps, including deposition of an ITO film on a glass surface by sputtering, then baking the ITO film above its melting point to create a conductive ITO layer, and finally etching the conductive ITO layer by photo or laser lithography to form a sensing circuit. Every manufacturing step adds to the cost of the final device, resulting from materials and elongated manufacturing time. Since every step may have risks for causing defects, losses or decreasing production yield further contribute to the overall cost. In addition, as the size of the capacitive touch screen increases, so does its weight since the typical touch screen comprises two layers of glass.
To reduce the cost and the weight of the touch screen, several different touch screen structures are being developed, such as sensor on-cell type touch screens, sensor in-cell type touch screens, glass lens/film sensor type touch screens, and sensor on glass lens or one glass solution (OGS) type touch screens. In these novel structures, main target is to reduce number of layers of glass incorporated into the system, thereby reducing the touch screen weight and costs.
However, there are still significant technical barriers for in-cell and on-cell type touch screens. For the on-cell type touch screens, the primary issue is the noise injected from the display module, such as liquid crystal display (LCD). As the touch sensor is structured to be closer and closer to the thin film transistor (TFT) switching elements of LCD, this noise substantially grows. In the case of in-cell type touch screen, the touch sensor is implemented within the TFT structure, which is complicated to manufacture, and therefore this type of touch screen is only used for a few high end applications today.
The glass lens/film type touch sensors are also manufactured by using two separate processes to prepare cover lenses and film sensors, and assembling these two components by using an optically clear adhesive.
The sensor on glass lens or one glass solution (OGS) approach may reduce the weight in overall device. This approach consolidates multilayer touch sensor system into a simpler structure and keeps supply chains intact for consumer electronics manufacturers. However, it still faces a number of technical challenges.
To be used as a glass lens, regular glass must be strengthened to prevent the breakage during the device use. The glass lens usually includes a silk screen printed decorative frame on its inner surface. This frame is used to hide the circuitry of the device. These two features of glass lens pose processing difficulties during the process scale up for commercialization. If the process scale up involves sputtering of an ITO layer on a large strengthened glass followed by patterning of the ITO layer, there may be substantial losses during cutting of the large strengthened glasses into small devices, decreasing the process yield. If the process involves small pieces of the strengthened glass, the productivity may dramatically drop.
Furthermore, the silk screen printed decorative frame usually has about 5 micrometers to 10 micrometers thickness. This frame prevents the ITO layer to form a uniform and continuous film during the ITO sputtering process across the glass and over the silk screen printed area. Any disruption in the conductive layer, at the frame to the glass transition regions, would cause device failures. This process may therefore be unsatisfactory.